Lactoferrin is a 78kD metal-binding single-chain glycoprotein found in milk and other exocrine secretions. It is the major protein component of human colostral whey, with concentrations as high as 6mg/ml. Since the human lactoferrin gene has been cloned, overexpression and large scale lactoferrin production are now possible.

Catalog #

L1021-74E

A great deal of structural information has been obtained about the lactoferrin molecule. It has been possible to relate this structural information to two striking in vitro properties of lactoferrin, its ability to bind a wide variety of metal ions with extremely high affinity, and its ability to bind to a number of different types of cells.

Lactoferrin also has bacteriostatic properties in vitro, which have been thought to derive from its powerful sequestration of iron; but a small bacteriostatic peptide obtained from lactoferrin digestion is remote from the iron binding site in the intact molecule.

Lactoferrin from motherís milk can be absorbed to some extent by the nursing infant and excreted in the infantís urine, but no reproducible published evidence has established any in vivo activity of lactoferrin.

Three striking in vitro properties of lactoferrin may be of importance to its biological function

its ability to bind and release a wide variety of metal ions, especially ferric iron (Fe), its ability to bind cations, and its binding to a number of different types of cells. In milk, as in other secretions, lactoferrin is mostly iron-free, with a saturation level of about 8 to 10 percent. In iron-free form it has pronounced bacteriostatic properties in vitro, probably dependent on its ability to bind adventitious iron extremely tightly, so depriving bacteria of iron essential for growth. The bacteriostatic properties of human milk are thought to derive largely from the high concentrations of lactoferrin present. In addition, sequestration of iron by lactoferrin inhibits iron-catalyzed free radical damage to cells. For these reasons, and because of its widespread occurrence in an frequent association with species such as lysozyme and immunoglobulins, lactoferrin is regarded as a component of the bodyís defense mechanisms. Lactoferrin is also a component of neutrophil secretory granules.

The lactoferrin molecules of different tissues and secretions appear to be identical in structure and function, and the cDNA sequence of leukocyte lactoferrin matches the amino acid sequence of milk lactoferrin. Lactoferrin is a member of the transferrin family of iron binding proteins, which includes serum transferrin, ovotransferrin, and the membrane-associated melanotransferrin. Lactoferrin also bears a striking relationship to a sulfate-binding protein of Salmonella typhimurium.

Lactoferrin has the capacity to bind reversibly two Fe ions concomitantly with two carbonate (C03=) or bicarbonate (HC03-) anions. Three features of metal binding by lactoferrin are particularly remarkable

the synergistic relationship between cation and anion binding, the extremely tight binding of iron, and the existence of mechanisms for the release of tightly-bound iron. Other metals can be substituted for iron in the two specific sites; those of similar size and charge (Ga, A1, Cr, Mn, Co) bind with affinities close to that of Fe, but even much larger cations such as lanthanides and some actinides (Th, Pu) can be accommodated.

Likewise, although CO3= is the anion of highest affinity, other anions with a carboxylate group, some quite bulky, can be substituted for it. The two lactoferrin structural cavities in which Fe and the anion are bound seem much larger than necessary for this function. To some this has suggested that lactoferrin may function to bind anionic toxins and xenobiotics. All the Mn in human milk is bound to lactoferrin, and lactoferrin has been suggested to have a role in Zn binding and heavy metal absorption. The physiological importance of transferrin in A1 binding and its proposed therapeutic use in detoxification may also apply to lactoferrin.

The ability of lactoferrin to bind to a variety of normal and leukemic blood cells has led to a suggestion that the lactoferrin released by neutrophilic leukocytes plays a role in modulating the immune and inflammatory responses. Lactoferrin promotes the aggregation of neutrophils and their adhesion to epithelial cells, and may be the agent that causes neutrophils to accumulate at inflammatory sites. Lactoferrin in its iron-saturated form is a highly active inhibitor of myelopoiesis, leading to the suggestion that lactoferrin might be useful in the treatment of leukemia.

Other observations that focus on the ability of lactoferrin to interact with cells include its activity as an essential growth factor for lymphocyte cell lines, its partial sequence homology with a group of lymphoma transforming proteins, its interference in the receptor-mediated uptake of chylomicron remnants into the liver, and the observation that some antibacterial activities of lactoferrin depend on actual contact with bacteria rather than simple sequestration of iron.

Source

Human Lactoferrin, Apo Form, from human breast milk.

Storage and Stability

May be stored at 4°C for short-term only. For long-term storage, store at -20°C. Aliquots are stable for at least 6 months at -20°C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Further dilutions can be made in assay buffer.

Molecular Weight

78kD

Source

Human milk

Purity

98% (SDS-PAGE).

Concentration

~2mg/ml

Form

Supplied as a liquid in distilled water.

Important Note

This product as supplied is intended for research use only, not for use in human, therapeutic or diagnostic applications without the expressed written authorization of United States Biological.